1. Field of the Invention
The present invention relates to an inverse photo development process resulting from optical photomicroscopy in darkfield illumination mode used in the examination and evaluation of LSIC/VLSIC (large scale and vary large scale integrated circuit) patterns and materials elements on a silicon chip. Such devices are multilayer structures defined and fabricated with aid of photomask patterns and successive etch-back materials process deposition steps by which these levels are precisely controlled (e.g., insulating oxides, doping pattern levels, implantations and diffusions, polysilicon gate patterns and metallization interconnects).
2. Description of the Prior Art
It is often necessary to physically evaluate LSIC/VLSIC devices for the purposes of product reliability assurance, validation of physical design and identification of device structural patterns. The most frequently used tool is a laboratory type optical microscope providing brightfield, contrast interference and darkfield modes of illumination; another tool is a scanning electron microscope (SEM) which is accurate and specific but more costly to use. It has been found that in the darkfield mode of optical examination of VLSIC chips the physical microstructure patterns corresponded more closely to photomask steps. The same pattern examples when viewed in the brightfield or contrast interference modes display unwanted fringe pattern effects resulting in distortions as to the physical definition of structures and materials when exposed in successive chemical etching steps while exposing the desired level for identification.